This invention relates to hearing aids, and particularly to improvements in the earmolds of the horn or resonating type used in certain types of hearing aid systems.
It is known that best improvements in hearing are obtained by the use of hearing aids which provide a frequency dependent, variable amplitude output which matches the frequency variable hearing impairment characteristic of the hearing aid user. While frequency dependent, amplitude output sound shaping is possible with present day electronic amplifiers, it is known that the earmold portion of the hearing aid plays a significant role in the overall sound characteristic of the system. Because of this, it is the practice, in some instances, to use earmolds which are designed to resonate at selected frequencies to assist in the desired output sound signal shaping.
One earmold, for example, known as a Killion earmold (discussed, for example, in various articles in the October 1980 issue of the magazine, Hearing Instruments, Vol. 31, No. 10), is designed to function as an acoustic horn using the length and the cross-sectional area of the bore through the earmold as the design parameters to select the desired resonant frequency of the earmold.
One problem with such earmolds, however, as discussed on page 30 of the magazine, is that it is often not possible, owing to the anatomical characteristics of individual patients, to design an earmold which is both comfortable to the user and which has the necessary dimensions to provide a frequency characteristic which best matches the needs of the user. A further problem, not discussed in the magazine, results from the fact that the sound characteristics of the hearing aid are affected by the particular sound chamber formed by the combination of the earmold and the ear canal of the user. Thus, regardless of how carefully the earmold fitting process is performed and the earmold designed, it generally occurs that the final sound characteristics cannot be fully determined until the earmold is completed and tested on the patient. While such testing quite frequently reveals that the intended results have not been attained, with known earmolds few adjustments or modifications of the finished earmold can be made to better match their sound characteristics with the hearing requirements of the user.